Tape drives typically utilize an actuator mechanism to position the read/write head over the appropriate tracks while the tape is moving. Current read/write head positioning devices used in magnetic tape drives often incorporate a dual stage actuator design. One actuator provides coarse positioning to move the read/write head between data bands. The other actuator provides fine positioning to maintain alignment between the read/write head and the data tracks. In use, the coarse positioning actuator first moves the read/write head to the general vicinity on the tape and then the fine positioning actuator is used for track following while the tape is in motion. The two actuators are usually mounted in a “piggyback” arrangement with the fine position actuator riding on the coarse position actuator.
The coarse positioning actuator is typically a linear stage driven by a stepper motor. Stepper motors have the ability to move the linear stage anywhere across the width of the magnetic tape at modest speeds. However, most stepper motors lack the accuracy and bandwidth necessary to maintain alignment between the read/write head and the data tracks as the magnetic tape moves across the face of the read/write head.
The fine positioning actuator is typically a voice coil motor (VCM) mounted on the linear stage and held at a rest position by some type of spring. A VCM actuator provides micron to submicron precision positioning at a bandwidth of hundreds to thousands of hertz. However, a single voice coil and spring combination that can meet the fine positioning requirements across the full width of the tape is expensive and unnecessary. Accordingly, virtually all current tape drives use some combination of a coarse positioning actuator and a fine positioning actuator.
In typical VCM actuator designs for tape drives, the housing must fully encapsulate the magnet and pole piece of the VCM to protect the head from exposure to the stray field caused by the magnet. A beam subassembly, which forms the connection between the coil and the head must pass through a housing that acts as part of the VCM magnetic flux path. This has a result of limiting access to the coil within the housing, requiring the physical connection between the coil and the read/write head to be made up of multiple parts, as well as assembled in multiple steps. This in turn increases both manufacturing and assembly cost.
FIG. 1 illustrates a typical fine positioning VCM assembly 100 for a tape drive system. The VCM assembly 100 includes a bottom cover 102 and a housing 104, which together act to contain the magnetic flux of the VCM so that the flux does not interfere with nearby electronic components, especially the transducers on the head. A beam 106 supports the head in a support cradle 108, thereby allowing the VCM to position the head. The beam 106 is formed of multiple parts, including a top portion 110 and a support plate 112. The top portion 110 of the beam must be inserted through apertures in the housing 104 and coupled to the support plate 112. A coil 114 is then attached to the support plate 112 of the beam 106. A pole piece 116 and magnet 118 are installed to complete the VCM. The bottom cover 102 is attached to the housing 104.
As should now be apparent, a typical VCM assembly 100 contains many parts, and requires a substantial amount of precision assembly. What is needed is a way to simplify assembly of a VCM, thereby reducing both cost and complexity. What is also needed is a way to reduce the number of unique parts needed to create a fine positioning actuator. These unresolved problems and deficiencies are clearly felt in the art and are solved by this invention in the manner described below.